The present invention relates to a coating composition, and more particularly to a coating composition remarkably excellent in storage stability in comparison with conventional coating compositions, which can be suitably used as a coating material for a substrate such as metal.
Recent years, in electrical or electronic industry, there have been desired transparent coating materials having heat resistance, corrosion resistance, scratch resistance, weather resistance, and the like. Examples of the transparent coating materials are, for instance, transparent coating materials which have been used to protect reflectors of lighting equipments or thermal apparatuses, and the like.
In order to satisfy the above-mentioned requirements, there have hitherto been studied organic paints such as silicone resin and fluorine-containing resin, inorganic paints such as alkaline metal silicate, and the like. However, there has not yet been provided a coating composition sufficiently having the above properties. That is, with respect to the former, there are some defects in heat resistance, weather resistance, corrosion resistance and scratch resistance, and with respect to the latter, there are some defects in that an alkaline material remained in the coating material reacts with carbon dioxide gas present in air and a carbonate is deposited on the surface of the coating, which is so called "efflorescence", with the passage of time, and that the coating composition is poor in workability for coating.
It has been studied to use silica-organosilane coating compositions having abrasion resistance as a coating materials which are mainly coated on the surface of a plastic material. However, these coating materials are poor in storage stability and workability for coating. Accordingly, various investigations have been made to solve these problems. However, there has not yet been produced a coating material having the sufficient properties of matter. For instance, silica-organosilane compositions for coating having abrasion resistance are disclosed in Japanese Examined Patent Publication No. 39691/1977, Japanese Examined Patent Publication No. 18626/1981, and the like. However, these compositions are poor in workability for coating and storage stability since they contain a large amount of water derived from aqueous colloidal silica.
A composition for coating which solves the above-mentioned problems is proposed in Japanese Unexamined Patent Publication No. 68377/1984. The workability for application of the composition has been surely somewhat improved by distilling water from the composition. However, the composition has not yet been satisfied with storage stability. The process for preparing the composition is complicated since there is a necessity to distill water from the composition, and there are some defects in the composition that turbidity is easily generated, that the viscosity is easily increased and that the transparency of the coating film is deteriorated.
In consideration of the above-mentioned problems of prior art, in the course of studying to give a composition not only having suffient properties of matter such as heat resistance, surface hardness, chemical resistance, abrasion resistance, scratch resistance, stain resistance and weather resistance, but also having excellent storage stability and workability for coating, it has been found that the storage stability of the composition is remarkably improved by using as a solvent, a solvent containing a specified amount of ethylene glycol monobutyl ether in comparison with that of the conventional coating compositions, and the present invention has been accomplished.